Learning-based feature detection processing device and method

ABSTRACT

A learning apparatus includes an image generator, a feature point extractor, a feature value calculator, and a classifier generator. The image generator generates, from an input image, images having differing scale coefficients. The feature point extractor extracts feature points from each image generated by the image generator. The feature value calculator calculates feature values for the feature points by filtering the feature points using a predetermined filter. The classifier generator generates one or more classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a learning apparatus and method, a recognition apparatus and method, a program, and a recording medium. More particularly, the present invention relates to a learning apparatus and method, a recognition apparatus and method, a program, and a recording medium whereby target objects can be more reliably detected from an image.

2. Description of the Related Art

In the related art, technology for detecting humans from images has been researched and developed, primarily for security or in-vehicle applications. (See for example: Navneet Dalal and Bill Triggs, “Histograms of Oriented Gradients for Human Detection”, CVPR2005; and B. Wu and R. Nevatia, “Detection of multiple, partially occluded humans in a single image by bayesian combination of edgelet part detectors”, In Proc. 10th Int. Conf. Computer Vision, 2005.) In such literature, contour feature values obtained by edge detection are used as the primary feature values for detecting (i.e., recognizing) humans from images. With such technologies, many variations of contour feature values obtained by edge detection are defined as new feature values, and human recognition is conducted therewith.

For example, in the technology proposed by Dalal and Triggs feature values are obtained by taking histograms oriented within small regions of edges. By using such feature values, the technology has the advantage of being more resilient to some degree of contour distortion and similar factors.

SUMMARY OF THE INVENTION

In the above methods for detecting humans or similar figures from an image, contour features are utilized to detect humans or similar figures. However, such methods significantly increase the computational complexity involved, and it is thus problematic to detect humans in real-time, for example.

In light of such circumstances, there is desire for technology enabled to detect target objects such as humans in real-time by improving calculation efficiency.

A learning apparatus in accordance with an embodiment of the present invention includes: generating means configured to generate, from an input image, images having differing scale coefficients; extracting means configured to extract feature points from each image generated by the generating means; calculating means configured to calculate feature values for the feature points by filtering the feature points using a predetermined filter; and classifier generating means configured to generate one or more classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values.

The predetermined filter may be a derivative function having a predetermined Gaussian width.

The calculating means may execute convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, and then calculate the sum of absolute values of the computational results.

The calculating means may execute convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, and then calculate the maximum absolute value of the computational results.

The scale coefficients of the images used when classifying the predetermined target object using the one or more classifiers may be identical to the scale coefficients in the generating means.

The input image may be an image containing an image of a predetermined hand shape, or alternatively, an image not containing an image of a hand. The one or more classifiers may be classifiers for detecting a predetermined hand shape.

A learning method in accordance with an embodiment of the present invention includes the steps of: generating, from an input image, images having differing scale coefficients; extracting feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and generating one or more classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values.

A computer-readable program in accordance with an embodiment of the present invention executes processing including the steps of: generating, from an input image, images having differing scale coefficients; extracting feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and generating one or more classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values.

In a learning apparatus, method, and program in accordance with embodiments of the present invention, images having differing scale coefficients are generated from an input image. Feature points are extracted for each of these images, which are then filtered using a predetermined filter. The results are taken to be feature values. One or more classifiers for detecting a predetermined target object from an image are then generated by means of statistical learning using the feature values.

A recognition apparatus in accordance with another embodiment of the present invention includes: generating means configured to generate, from an input image, images having differing scale coefficients; extracting means configured to extract feature points from each image generated by the generating means; calculating means configured to calculate feature values for the feature points by filtering the feature points using a predetermined filter; and detecting means configured to detect a predetermined target object from the input image by substituting the feature values into one or more classifiers obtained by statistical learning and used for detecting a target object from an image.

The predetermined filter may be a derivative function having a predetermined Gaussian width.

The calculating means may execute convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, and then calculate the sum of absolute values of the computational results.

The calculating means may execute convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, and then calculate the maximum absolute value of the computational results.

The one or more classifiers may be classifiers for detecting a predetermined hand shape. The input image may be stored when the predetermined hand shape is detected by the detecting means.

A recognition method in accordance with an embodiment of the present invention includes the steps of: generating, from an input image, images having differing scale coefficients; extracting feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and detecting a predetermined target object from the input image by substituting the feature values into one or more classifiers obtained by statistical learning and used for detecting a target object from an image.

A program in accordance with an embodiment of the present invention causes a computer to execute processing including the steps of: generating, from an input image, images having differing scale coefficients; extracting feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and detecting a predetermined target object from the input image by substituting the feature values into one or more classifiers obtained by statistical learning and used for detecting a target object from an image.

In a recognition apparatus, method, and program in accordance with embodiments of the present invention, images having differing scale coefficients are generated from an input image. Feature points are extracted for each of these images, which are then filtered using a predetermined filter. The results are taken to be feature values. The feature values are substituted into one or more classifiers for detecting a predetermined target object from an image, and the predetermined target object is detected.

According to an embodiment of the present invention, real-time detection of target objects such as humans, as well as learning for the same, is possible with improved calculation efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a human classification system to which an embodiment of the present invention has been applied;

FIG. 2 illustrates an exemplary detailed configuration of a clothing classifier generator;

FIG. 3 illustrates an exemplary detailed configuration of a contour feature value calculator;

FIG. 4 explains steerable filters;

FIG. 5 illustrates the results of filtering an image;

FIG. 6 is a flowchart explaining learning processing;

FIG. 7 is a flowchart explaining clothing classifier generation processing;

FIG. 8 is a flowchart explaining contour feature value calculation processing;

FIG. 9 explains clothing feature point extraction;

FIG. 10 explains clothing feature values;

FIG. 11 explains clothing feature value sampling on a per-pair basis of clothing feature points;

FIG. 12 explains weak classifier configuration;

FIG. 13 explains clothing feature point pairs;

FIG. 14A explains contour feature point extraction;

FIG. 14B explains contour feature point extraction;

FIG. 15 is a flowchart explaining human detection processing;

FIG. 16 illustrates an exemplary target object recognition results display;

FIG. 17 explains the generation of a classifier for detecting a hand of predetermined shape;

FIG. 18 illustrates an example of a hand image;

FIG. 19 illustrates a functional configuration of an image processing apparatus;

FIG. 20 explains the configuration of a recognition apparatus;

FIG. 21 is a flowchart explaining the operation of an image processing apparatus; and

FIG. 22 is a block diagram illustrating an exemplary configuration of a computer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[System Configuration]

FIG. 1 is a block diagram illustrating an exemplary configuration of a human classification system to which an embodiment of the present invention has been applied. The human classification system includes a learning apparatus 11, a classifier recording unit 12, and a recognition apparatus 13, and recognizes regions in an input image containing a target object in the form of an image of a human.

On the basis of input learning images, the learning apparatus 11 generates classification feature values and an ensemble classifier, which are used in the recognition apparatus 13 when determining whether or not there exists a target object in the image. The classification feature values and ensemble classifier are recorded in the classifier recording unit 12. Using the classification feature values and the ensemble classifier recorded in the classifier recording unit 12, the recognition apparatus 13 determines whether or not a target object (i.e., an image of a human) exists in the input image, and outputs the classification result.

The learning apparatus 11 includes a image pyramid generator 20, a clothing feature point extractor 21, a clothing feature value calculator 22, a clothing classifier generator 23, a contour feature point extractor 24, a contour feature value calculator 25, a contour classifier generator 26, and an ensemble classifier generator 27.

The image pyramid generator 20 generates a plurality of images having respectively different resolutions from an input learning image, and then supplies the images as an image pyramid to the clothing feature point extractor 21 and the contour feature point extractor 24. For example, an image pyramid having eight layers of resolution from level L1 to level L8 may be generated, wherein the L1 image has the highest resolution, and wherein the resolution of the images decrease in order from L1 to L8.

From each image constituting the image pyramid generated by the image pyramid generator 20 (each image also being referred to as a learning image), the clothing feature point extractor 21 extracts several pixels in that learning image as clothing feature points, which are used when generating a clothing classifier. The extracted clothing feature points are supplied to the clothing feature value calculator 22 together with the learning images. Herein, a clothing classifier is a strong classifier made up of a plurality of weak classifiers, and generated by statistical learning. The clothing classifier, utilizing the features of a person's clothing, is used when determining whether or not a human image region exists in the input image.

For each clothing feature point received from the clothing feature point extractor 21, the clothing feature value calculator 22 creates a single pair by pairing that clothing feature point with another clothing feature point. In addition, on the basis of the learning images received from the clothing feature point extractor 21, the clothing feature value calculator 22 calculates a clothing feature value for each pair of clothing feature points, which indicates the texture distance between two arbitrary regions. The clothing feature values thus solved for and the learning images are supplied to the clothing classifier generator 23.

On the basis of the learning images and the clothing feature values supplied from the clothing feature value calculator 22, the clothing classifier generator 23 conducts statistical learning processing according to Adaboost, for example, and generates a clothing classifier for recognizing a target object (i.e., a person). In addition, the clothing classifier generator 23 supplies the generated clothing classifier to the ensemble classifier generator 27.

From each image constituting the image pyramid generated by the image pyramid generator 20 (each image also being referred to as a learning image), the contour feature point extractor 24 extracts several pixels in that learning image as contour feature points, which are used when generating a contour classifier. The extracted contour feature points and the learning images are supplied to the contour feature value calculator 25. Herein, a contour classifier is a strong classifier made up of a plurality of weak classifiers, and generated by statistical learning. The contour classifier, utilizing a person's contours, is used when determining whether or not a human image region exists in the input image.

On the basis of the learning images received from the contour feature point extractor 24, and by means of filter processing using a steerable filter, for example, the contour feature value calculator 25 calculates a contour feature value for each contour feature point, which indicates the extracted contours. The contour feature values thus solved for and the learning images are supplied to the contour classifier generator 26. On the basis of the learning images and the contour feature values supplied from the contour feature value calculator 25, the contour classifier generator 26 conducts statistical learning processing according to Adaboost, for example, and generates a contour classifier for recognizing a target object (i.e., a person). In addition, the contour classifier generator 26 supplies the generated contour classifier to the ensemble classifier generator 27.

The ensemble classifier generator 27 combines the clothing classifier from the clothing classifier generator 23 with the contour classifier from the contour classifier generator 26 to generate an ensemble classifier, which is supplied to and recorded in the classifier recording unit 12. In addition, the clothing feature values for the clothing feature point pairs and the contour feature values for the contour feature points, which are used when recognizing a target object using the ensemble classifier, are also supplied to the classifier recording unit 12 by the ensemble classifier generator 27 and recorded as classification feature values.

The recognition apparatus 13 includes a clothing feature point extractor 31, a clothing feature value calculator 32, a contour feature point extractor 33, a contour feature value calculator 34, a classification calculator 35, and a classification result output unit 36. Each of the components from the clothing feature point extractor 31 to the contour feature value calculator 34 in the recognition apparatus 13 respectively processes an input image in which a target object is to be recognized similarly to the clothing feature point extractor 21, the clothing feature value calculator 22, the contour feature point extractor 24, and the contour feature value calculator 25 in the learning apparatus 11. For this reason, detailed description of the above components is omitted.

The classification calculator 35 reads the classification feature values and the ensemble classifier recorded in the classifier recording unit 12. In addition, the classification calculator 35 substitutes into the ensemble classifier and computes information corresponding to the clothing feature values received from the clothing feature value calculator 32 and the contour feature values received from the contour feature value calculator 34. The classification result output unit 36 acquires the computational from the classification calculator 35, and on the basis of that computational result, outputs a classification result indicating whether or not a target object was recognized in the input image.

[Configuration of Clothing Classifier Generator]

FIG. 2 is a block diagram illustrating a more detailed exemplary configuration of the clothing classifier generator 23 shown in FIG. 1. The clothing classifier generator 23 includes a sampling unit 51, a weighting unit 52, a sorter 53, a classifier configuration unit 54, a classifier selector 55, and a weight updater 56.

The sampling unit 51 samples M clothing feature values from the clothing feature values for pairs of clothing feature points at respectively identical positions in a plurality of learning images. Sampling is conducted for each pair of clothing feature points and according to per-learning-image weights set by the weighting unit 52. The M clothing feature values thus sampled are supplied to the sorter 53.

The sorter 53 sorts the M clothing feature values thus sampled for each pair clothing feature points in ascending or descending order, and supplies the sorted result to the classifier configuration unit 54.

On the basis of hit/miss information indicating whether or not a target object to be recognized is contained in the learning image from which a particular clothing feature value was extracted, the classifier configuration unit 54 controls an error rate calculator 54 a while varying the threshold value for each of the per-pair clothing feature values sorted in ascending or descending order. The error rates are thus calculated, and threshold values are set such that the error rates are minimized (these threshold values are set as weak classifiers). In addition, the classifier configuration unit 54 supplies the error rate for each weak classifier to the classifier selector 55.

The hit/miss information (i.e., a label) indicating whether or not the target object is contained in a learning image is appended to that learning image. On the basis of the hit/miss information appended to the learning images supplied from the clothing feature value calculator 22, the classifier configuration unit 54 configures weak classifiers.

The classifier selector 55 selects the weak classifier with the minimum error rate from among the weak classifiers, updates the clothing classifier made up of the weak classifiers, and supplies clothing feature values corresponding to the final clothing classifier and each weak classifier to the ensemble classifier generator 27. In addition, the classifier selector 55 calculates a reliability factor on the basis of the error rate of the selected weak classifier, and supplies the result to the weight updater 56.

On the basis of the supplied reliability factor, the weight updater 56 re-calculates weights for each learning image, additionally normalizes and updates the weights, and supplies the updated result to the weighting unit 52. On the basis of the updated weight result supplied by the weight updater 56, the weighting unit 52 sets the weights for each learning image.

[Configuration of Contour Feature Value Calculator]

FIG. 3 illustrates a more detailed exemplary configuration of the contour feature value calculator 25 shown in FIG. 1. The contour feature value calculator 25 includes a first-order filter processor 61, a second-order filter processor 62, a third-order filter processor 63, and a feature value generator 64. In addition, the learning images from the contour feature point extractor 24 are respectively supplied to each component from the first-order filter processor 61 to the feature value generator 64, while the contour feature points are respectively supplied to each component from the first-order filter processor 61 to the third-order filter processor 63.

The first-order filter processor 61 extracts feature values by filtering each supplied contour feature point using a first-order derivative function G₁ of a Gaussian function G, and supplies the result to the feature value generator 64. Herein, the Gaussian function G and the first-order derivative function G₁ are given in the following Eqs. 1 and 2.

$\begin{matrix} {{Eq}.\mspace{14mu} 1} & \; \\ {G = {\mathbb{e}}^{- \frac{x^{2} + y^{2}}{2\sigma^{2}}}} & (1) \\ {{Eq}.\mspace{14mu} 2} & \; \\ {{G_{1}(\theta)} = {{{\cos(\theta)}{G_{1}\left( {0{^\circ}} \right)}} + {{\sin(\theta)}{G_{1}\left( {90{^\circ}} \right)}}}} & (2) \end{matrix}$

In Eq. 1, σ represents the Gaussian width. In Eq. 2, θ represents an arbitrary angle indicating the desired direction in which to apply the filter.

For example, the first-order filter processor 61 may vary the Gaussian width σ of the Gaussian function G among three preset values (such as Gaussian widths σ₁=1, σ₂=2, and σ₃=4, for example), and then evaluate Eq. 2 in four predetermined directions (θ₁, θ₂, θ₃, and θ₄, for example) for each Gaussian width σ.

It should be appreciated that the direction θ is not limited to four directions, and that eight directions may also be used (such as the directions obtained when dividing pi equally in eight directions). Furthermore, although the related art conducts processing using a plurality of Gaussian widths as described above, just a single Gaussian width may be prepared for the present embodiment, as described later. In other words, varying the Gaussian width may be omitted. Thus, although the above states that the Gaussian width σ is varied among three preset values and Eq. 2 is evaluated in four predetermined directions for each Gaussian width σ, in the present embodiment, Eq. 2 may simply be evaluated in four predetermined directions for a single Gaussian width σ that has been set.

Since the calculations for each of a plurality of Gaussian widths may be omitted, it is possible to reduce the computational complexity. The same is also true for other filters, such as the second-order filter processor 62 and the third-order filter processor 63.

The second-order filter processor 62 extracts feature values by filtering each supplied contour feature point using a second-order derivative function G₂ of a Gaussian function G, and supplies the result to the feature value generator 64. Eq. 3 expresses the second-order derivative function G₂, where θ represents an arbitrary angle.

Eq. 3 G ₂(θ)=k ₂₁(θ)G ₂(0°)+k ₂₂(θ)G ₂(60°)+k ₂₃(θ)G ₂(120°)  (3)

The coefficient k_(2i)(0) (where i=1, 2, 3) in Eq. 3 represents the function expressed by the following Eq. 4.

Eq.  4 $\begin{matrix} {{k_{2i}(\theta)} = {\frac{1}{3}\left\{ {1 + {2\;{\cos\left( {2\left( {\theta - {\theta\; i}} \right)} \right)}}} \right\}}} & (4) \end{matrix}$

The second-order filter processor 62 may, for example, evaluate Eq. 3 in four predetermined directions (θ₁, θ₂, θ₃, and θ₄, for example) for a predetermined Gaussian width σ of the Gaussian function G.

The third-order filter processor 63 extracts feature values by filtering each supplied contour feature point using a third-order derivative function G₃ of a Gaussian function G, and supplies the result to the feature value generator 64. Eq. 5 expresses the third-order derivative function G₃, where θ represents an arbitrary angle.

Eq. 5 G ₃(θ)=k ₃₁(θ)G ₃(0°)+k ₃₂(θ)G ₃(45°)+k ₃₃(θ)G ₃(90°)+k ₃₄(θ)G ₃(135°)  (5)

The coefficient k_(3i)(θ) (where i=1, 2, 3) in Eq. 5 represents the function expressed by the following Eq. 6.

Eq.  6 $\begin{matrix} {{k_{3i}(\theta)} = {\frac{1}{4}\left\{ {{2\;{\cos\left( {\theta - {\theta\; i}} \right)}} + {2\cos\;\left( {3\left( {\theta - {\theta\; i}} \right)} \right)}} \right\}}} & (6) \end{matrix}$

The third-order filter processor 63 may, for example, evaluate Eq. 5 in four predetermined directions (θ₁, θ₂, θ₃, and θ₄, for example) for a predetermined Gaussian width σ of the Gaussian function G.

The feature value generator 64 receives the feature values for each contour feature point, calculated in four directions and respectively supplied from the first-order filter processor 61, the second-order filter processor 62, and the third-order filter processor 63. The supplied total of 12 feature values (four directions in three orders) are collectively taken to be the contour feature value for each contour feature point.

In addition, since each filter processor is supplied with a plurality of images at different resolutions from the image pyramid generator 20, feature values from each image calculated in the four directions θ for each contour feature point are supplied to the feature value generator 64. The supplied feature values depend on the number of images generated by the image pyramid generator 20. For example, when eight images from level 1 to level 8 are generated, eight sets of feature values calculated in the four directions θ for each contour feature point are supplied.

The feature value generator 64 supplies both the generated contour feature value and the supplied learning images to the contour classifier generator 26.

Thus, in the contour feature value calculator 25, derivatives of a Gaussian function are taken to obtain filters (i.e., basis functions) with directional (θ) selectivity. The obtained filters are used to extract feature values (i.e., contours) that differ for each order of the derivative, and which are taken to be the contour feature values.

As shown in FIG. 4, when steerable filters are used for contour feature value extraction, if filters are prepared having different directions θ and Gaussian widths a, then a linear combination of these filters can be used to create a filter of arbitrary direction θ, or in other words, the derivative functions G_(n) (wherein n=1, 2, 3) of the Gaussian function G.

The topmost images in the horizontal rows shown on the right side of FIG. 4 represent the first-order derivative function G₁(θ) for a Gaussian width σ equal to 1, illustrating θ values of 0, ⅛*pi, 2/8*pi, ⅜*pi, 4/8*pi, ⅝*pi, 6/8*pi, and ⅞*pi, in order from left to right.

Similarly, the horizontal rows shown on the right side of FIG. 4 respectively represent, in order from the second row from the top and proceeding downwards, the first-order derivative function G₁(θ) for a Gaussian width σ equal to 2, the first-order derivative function G₁(θ) for a Gaussian width σ equal to 4, the second-order derivative function G₂(θ) for a Gaussian width σ equal to 1, the second-order derivative function G₁(θ) for a Gaussian width σ equal to 2, the second-order derivative function G₂(θ) for a Gaussian width σ equal to 4, the third-order derivative function G₃(θ) for a Gaussian width σ equal to 1, the third-order derivative function G₃(θ) for a Gaussian width σ equal to 2, and the third-order derivative function G₃(θ) for a Gaussian width σ equal to 4. Furthermore, the images in each row illustrate the corresponding derivative function with θ values of 0, ⅛*pi, 2/8*pi, ⅜*pi, 4/8*pi, ⅝*pi, 6/8*pi, and ⅞*pi, in order from left to right.

For example, two filters shown on the left side of FIG. 4, the first-order derivative function G₁(0°) and the first-order derivative function G₁(90°), can be used to express the first-order derivative function G₁(θ) for each direction θ shown in the second row from the top on the right side of FIG. 4. Similarly, the second-order derivative functions G₂ on the left side of FIG. 4 can be used to express the second-order derivative function G₂(θ) for each direction θ shown in the fifth row from the top on the right side of FIG. 4. The third-order derivative functions G₃ on the left side of FIG. 4 can be used to express the third-order derivative function G₃(θ) for each direction θ shown in the eighth row from the top on the right side of FIG. 4. In other words, given a number of basis functions one greater than their dimensionality, a derivative function of arbitrary direction in the same dimensionality can be expressed by a linear combination of the basis functions.

FIG. 5 illustrates the results obtained by filtering an image depicting a human using derivative functions of a Gaussian function G. In FIG. 5, the images to be filtered is shown on the left, the filters are shown in the center, and the post-filter images are shown on the right.

The images shown on the left side of FIG. 5 are two images constituting an image pyramid, and have different resolutions. As described earlier, the image pyramid generator 20 generates images with different resolutions from levels L1 to L8, for example. On the left side of FIG. 5, the L1 image 101 and the L2 image 102 from such an image pyramid are shown by way of example.

The filters shown by way of example in the center of FIG. 5 are filters for the first-order derivative function G₁, the second-order derivative function G₂, and the third-order derivative function G₃, all having Gaussian widths a equal to 1. The filters shown by way of example in the center of FIG. 5 are taken from a portion of the filters shown in FIG. 4.

When filters from among those shown in the center of FIG. 5 (such as the filters for the third-order derivative function G₃, for example) are used to filter the images shown on the left side of FIG. 5, the images shown on the right side of FIG. 5 are generated. In other words, if the image 101 is filtered by the filters of the third-order derivative function G₃, then the images 111-1 to 111-4 are generated. Likewise, if the image 102 is filtered by the third-order derivative filters, then the images 112-1 to 112-4 are generated.

The images 111-1 to 111-4 have been respectively filtered using the filters of the third-order derivative function G₃ with a Gaussian width σ equal to 1 (σ=1). Thus, the images 111-1 to 111-4 are the images obtained when filtering with filters having Gaussian widths σ equal to 1.

Similarly, the images 112-1 to 112-4 have been respectively filtered using the filters of the third-order derivative function G₃ with a Gaussian width σ equal to 1 (σ=1). Thus, the images 112-1 to 112-4 are the images obtained when filtering with filters having Gaussian widths σ equal to 1.

However, the images 112-1 to 112-4 are the images resulting from filtering the images 102. The images 102 are reduced versions of the images 101. In such a case, the images 112-1 to 112-4 can be taken to be equivalent to the images generated as a result of filtering using the filters of the third-order derivative function G₃ with a Gaussian width σ equal to 2 (σ=2). Stated differently, the images 112-1 to 112-4 are equivalent to the images generated when filtering the image 101 using the filters of the third-order derivative function G₃ with a Gaussian width σ equal to 2 (σ=2).

In other words, by filtering an image pyramid, it is possible to obtain images equivalent to those obtained when filtering a single image using multiple filters with different Gaussian widths. For example, if the computational complexity and processing load involved in filtering is compared between the case of filtering a single image using multiple filters prepared at each Gaussian width versus the case of filtering an image pyramid using a single filter prepared at a single Gaussian width, the filtering of the image pyramid using a single filter exhibits a significantly decreased computational complexity and processing load.

In other words, by generating an image pyramid and filtering it at a single Gaussian width, it is possible to significantly shorten processing time. Consequently, such a technique also shortens processing time when attempting to detect a human or other target object from an image, thereby making it possible to detect a target object from an image in real-time.

In this way, the contour feature value calculator 25 generates a plurality of images equivalent to those obtained when filtering with multiple filters having different Gaussian widths, and additionally generates an image obtained by averaging the plurality of generated images. The contours of a human can be confirmed from the average image thus generated, and thus human contours are suitably extracted from the image by filtering the image using the respective filters.

The internal configuration of the contour feature value calculator 34 in the recognition apparatus 13 shown in FIG. 1 is similar to that of the contour feature value calculator 25 shown in FIG. 3.

[Learning Process]

A learning process conducted in the learning apparatus 11 will now be described. A learning image is input into the learning apparatus 11, and when instructions to generate an ensemble classifier are issued, the learning apparatus 11 initiates the learning process and generates an ensemble classifier by means of statistical learning. Hereinafter, the learning process conducted by the learning apparatus 11 will be described with reference to the flowcharts shown in FIGS. 6 to 8.

In step S10, the image pyramid generator 20 generates an image pyramid from the input learning image. As described earlier, the image pyramid generator 20 generates, for example, an image pyramid having eight resolution layers from levels L1 to L8. The generated images are supplied to the clothing feature point extractor 21 and the contour feature point extractor 24. The clothing feature point extractor 21 and the contour feature point extractor 24 respectively set one image from the supplied image pyramid (i.e., the plurality of images having different resolutions) as the learning image to be processed, and execute the processing in steps S11 and thereafter. The processing in steps S11 and thereafter is repeatedly executed for each image in the plurality of images.

In step S11, the clothing feature point extractor 21 extracts clothing feature points from the supplied learning image, and then supplies the both the extracted clothing feature points and the learning image to the clothing feature value calculator 22.

In step S12, the clothing feature value calculator 22 uses the clothing feature points and the learning image supplied from the clothing feature point extractor 21 as a basis for pairing each clothing feature point with another clothing feature point.

In step S13, the clothing feature value calculator 22 calculates a clothing feature value for each pair of clothing feature points paired in step S12. The clothing feature values thus obtained are supplied to the clothing classifier generator 23.

For example, when the learning image shown in FIG. 9 is input into the clothing feature point extractor 21, the clothing feature point extractor 21 extracts clothing feature points from the learning image on the basis of a predetermined margin and sampling skip number. The circles on the learning image shown in FIG. 9 indicate the pixels taken as clothing feature points.

Herein, the margin refers to a number of pixels in the learning image that starts from the edge of the learning image and ends at the clothing feature point extraction region. The sampling skip number refers to an interval between two pixels in the learning image set as clothing feature points.

Consequently, when the margin is 5 pixels and the sampling skip number is 5 pixels, for example, the clothing feature point extractor 21 excludes from the learning image the region made up of pixels positioned within 5 pixels from the edge of the learning image, and sets the remaining region E11 as the target for clothing feature point extraction. Subsequently, the clothing feature point extractor 21 extracts pixels positioned 5 pixels apart from each other as the clothing feature points. In other words, in FIG. 9, the distance between adjacent clothing feature points is 5 pixels in both the vertical and horizontal directions, and each clothing feature point is a pixel within the region E11.

Next, the clothing feature value calculator 22 pairs each clothing feature point on the basis of a predetermined minimum radius and maximum radius. For example, for a minimum radius of R11 and a maximum radius of R12, when a given clothing feature point KT1 is targeted, the clothing feature value calculator 22 respectively pairs the clothing feature point KT1 with each of the clothing feature points whose distance from the clothing feature point KT1 is not less than the minimum radius R11 and not more than the maximum radius R12.

For example, in the case where there exist N clothing feature points whose distances from the clothing feature point KT1 are not less than the minimum radius R11 and not more than the maximum radius R12, N pairs are clothing feature points are obtained. The clothing feature value calculator 22 thus pairs all of the clothing feature points with other clothing feature points.

In addition, for each pair of clothing feature points obtained by the above pairing, the clothing feature value calculator 22 calculates the texture distance between regions of predetermined shape and size respectively centered about the clothing feature points constituting the pair. This calculated texture distance is taken to be the clothing feature value.

For example, consider the case of calculating the clothing feature value by taking the sum of absolute differences (SAD) for the pair made up of the clothing feature points KT1 and KT2 shown in FIG. 9. In this case, the clothing feature value calculator 22 defines a region TX1 to be a predetermined region centered about the clothing feature point KT1, and a region TX2 to be a region of the same size as the region TX1 and centered about the clothing feature point KT2. Subsequently, the clothing feature value calculator 22 calculates the sum of the absolute values of the differences between the pixel values of the pixels within the region TX1, and the pixel values of the corresponding pixels within the region TX2. The sum of the absolute differences thus calculated is taken to be the clothing feature value.

It should be appreciated that the clothing feature value is not limited to being the SSD, and may also be a value such as the sum of squared differences (SSD), or a normalized correlation.

In this way, the clothing feature value calculator 22 calculates a clothing feature value for each pair of clothing feature points extracted from the learning image. More specifically, a plurality of learning images are input into the learning apparatus 11, made up of several learning images containing the target object, and several learning images not containing the target object. Subsequently, clothing feature points are extracted and clothing feature values are calculated for each input learning image.

For example, consider the case wherein M learning images PI₁ to PI_(M) (where M is a natural number) are input into the learning apparatus 11. As shown in FIG. 10, a clothing feature value is obtained for each pair of clothing feature points in the M learning images PI_(i) (where 1≦i≦M).

In FIG. 10, a single square represents the clothing feature value for a single pair of clothing feature points. In addition, the columns of vertically-arranged squares in FIG. 10 represent sequences of clothing feature values obtained from the learning images PI_(i) (wherein 1≦i≦M). Each sequence contains a number of clothing feature values equal to the number of pairs of clothing feature points obtained from the given learning image PI_(i). In other words, the number of pairs of clothing feature points obtained from the learning image PI_(i) becomes the dimensionality of the clothing feature value for that learning image PI_(i).

The learning images herein refer to the respective images in an image pyramid, as described earlier. FIG. 10 illustrates the case wherein a three-image pyramid is generated from a single image, and wherein each of the three images in the pyramid is respectively processed. In other words, FIG. 10 illustrates the simple case of feature value vectors during learning when the number of multi-resolution levels has been set to 3.

In FIG. 10, scale refers to a scale coefficient. A scale coefficient is a reduction ratio indicating how the image size is scaled in the next level. For example, scale 1 indicates a scale coefficient of 1. A single column in FIG. 10 contains a number of clothing feature values equal to the number of pairs of clothing feature points respectively obtained from the plurality of learning images PI_(i) constituting the image pyramid.

In addition, at the bottom of the columns of clothing feature values for each learning image PI_(i) in FIG. 10, labels (i.e. hit/miss information) are shown indicating whether or not the target object is contained in that learning image PI_(i). For example, label “+1” shown at the bottom of the column of clothing feature values for the learning image PI₁ indicates that the target object is contained in the learning image PI₁, while the label “−1” shown at the bottom of the column of clothing feature values for the learning image PI_(M) indicates that the target object is not contained in the learning image PI_(M).

Returning now to the flowchart in FIG. 6, in step S13, the clothing feature values are calculated, and then in step S14, the clothing classifier generator 23 conducts the clothing classifier generation process to generate a clothing classifier.

The clothing classifier generation process corresponding to step S14 will now be described with reference to the flowchart in FIG. 7.

In step S51, the weighting unit 52 initializes, for example, all of the weights Wi for each learning image PI_(i) (where 1≦i≦M) shown in FIG. 10 to 1/M, while the classifier selector 55 respectively initializes a counter j to 1 and a clothing classifier R(x) made up of a sum of weak classifiers to 0.

Herein, i is a number for identifying the learning images PI_(i) shown in FIG. 10, where 1≦i≦M. As a result of the processing in step S51, the weights Wi for all learning images PI_(i) are all set to the same normalized weight (1/M). Additionally, the counter j is a number indicating a predetermined count for updating the clothing classifier R(x).

In step S52, the sampling unit 51 selects M clothing feature values for each pair of clothing feature points according to the weights of the learning images PI_(i) and from among the clothing feature values for the clothing feature points at the same respective positions in the plurality of learning images PI_(i). The M clothing feature values thus selected are supplied to the sorter 53.

For example, consider the case wherein clothing feature values from the M learning images from PI₁ to PI_(M) are supplied from the clothing feature value calculator 22 to the sampling unit 51, as shown in FIG. 11. In FIG. 11, the clothing feature values obtained from the learning images PI_(i) (wherein 1≦i≦M) are arranged in the horizontal direction. The numbers “+1” and “−1” shown to the left of the letters PI_(i) representing the learning images indicate the labels (i.e., hit/miss information) appended to each corresponding learning image PI_(i).

In other words, the sequence (A₁, A₂, A₃, . . . , A_(N)) arranged horizontally in the topmost row of FIG. 11 represents the respective clothing feature values for each pair of clothing feature points in the learning image PI₁. The number “+1” to the left of the text “PI₁” indicating the learning image PI₁ in FIG. 11 represents a label indicating that the target object is contained in the learning image PI₁.

Similarly, the sequence (B₁, B₂, B₃, . . . , B_(N)) arranged horizontally in the second row from the top of FIG. 11 represents the respective clothing feature values for each pair of clothing feature points in the learning image PI₂. The number “+1” to the left of the text “PI₂” indicating the learning image PI₂ in FIG. 11 represents a label indicating that the target object is contained in the learning image PI₂.

The sequence (C₁, C₂, C₃, . . . , C_(N)) arranged horizontally in the third row from the top of FIG. 11 represents the respective clothing feature values for each pair of clothing feature points in the learning image PI₃. The number “−1” to the left of the text “PI₃” in FIG. 11 represents a label indicating that the target object is not contained in the learning image PI₃. Furthermore, the sequence (M₁, M₂, M₃, . . . , M_(N)) arranged horizontally in the Mth row from the top of FIG. 11 represents the respective clothing feature values for each pair of clothing feature points in the learning image PI_(M). The number “−1” to the left of the text “PI_(M)” in FIG. 11 represents a label indicating that the target object is not contained in the learning image PI_(M).

Thus, in the example shown in FIG. 11, respective clothing feature values for N pairs of clothing feature points are obtained from a single learning image PI_(i). Furthermore, in FIG. 11, the M clothing feature values from A_(i) to M_(i) (where 1≦i≦M) arranged vertically form a single group Gr_(k). The clothing feature values belonging to a given group Gr_(k) are the clothing feature values for the pairs of clothing feature points at the same position in each learning image PI_(i).

For example, the group Gr₁ contains the vertically arranged clothing feature values from A₁ to M₁. The clothing feature value A₁ is calculated for a pair of clothing feature points in the learning PI₁. These two clothing feature points lie at the same positions on the learning image as the clothing feature points for the other clothing feature values belonging to the group Gr₁, such as the pair of clothing feature points in the learning image PI_(N) from which the clothing feature value M₁ is calculated. Hereinafter, when a pair of clothing feature points in a particular learning image PI_(i) is given, the pair will be designated as the pair k, indicating that a clothing feature value belonging to the group Gr_(k) (where 1≦k≦N).

When clothing feature values for each learning image PI_(i) shown in FIG. 11 are supplied to the sampling unit 51, the sampling unit 51 selects by lottery M clothing feature values for each pair k (i.e., for each group Gr_(k)) from the clothing feature values belonging to that group, and in accordance with the weights Wi of the learning images PI_(i). For example, the sampling unit 51 may select M clothing feature values from the clothing feature values from A₁ to M₁ belonging to the Gr₁, in accordance with the weights Wi. Thus, in the first process herein, all clothing feature values are selected in each group Gr_(k). Obviously, the same clothing feature values may also be selected multiple times in practice.

The weights Wi may also be used for calculating error for each pair of clothing feature points. In this case, error is calculated by multiplying the error values by data weighting coefficients (i.e., the weights Wi).

In step S53, the sorter 53 sorts the M clothing values selected for each of the N groups Gr_(k) (i.e., for each pair k) in ascending or descending order, and supplies the result to the classifier configuration unit 54. For example, the M clothing feature values selected from the clothing feature values belonging to the group Gr₁ in FIG. 11 are sorted in order.

In step S54, the classifier configuration unit 54 controls the error rate calculator 54 a while varying a threshold value for each group Gr_(k) (i.e., for each pair k of clothing feature points), on the basis of the hit/miss information (i.e., labels) appended to the learning images supplied from the clothing feature value calculator 22. By means of such control, the classifier configuration unit 54 calculates an error rate e_(jk) as shown in Eq. 7 given below, and sets the threshold value such that the error rate e_(jk) is minimized.

Herein, the threshold value th_(jk) for each pair k of clothing feature points becomes a single weak classifier f_(jk). The classifier configuration unit 54. The classifier configuration unit 54 supplies the error rate e_(jk) for each weak classifier f_(jk) to the classifier selector 55. In other words, for each of the N pairs k, N weak classifiers f_(jk) are respectively set, and an error rate e_(jk) is calculated for each of the N weak classifiers f_(jk). Herein, the weak classifiers f_(jk) are functions that output +1 when the target object for recognition is present, and −1 when the target object for recognition is not present.

For example, when j=1 and the clothing feature values L₁, A₁, C₁, B₁, . . . , M₁ for the pair k=1 of clothing feature points are arranged in ascending or descending order as shown in FIG. 12, the threshold value th₁₁ is set between the clothing feature values A₁ and C₁. In the range of values less than the threshold value th₁₁ (i.e., the range indicated by −1), the target object for recognition is not recognized, while in the range of values greater than the threshold value th₁₁ (i.e., the range indicated by +1), the target object for recognition is recognized. In this case, the clothing feature value A₁ circled by a broken line in FIG. 12 is a clothing feature value from a learning image containing the target object for recognition, and thus the clothing feature value A₁ is taken to be an error. In contrast, the clothing feature values C₁ and M₁ are clothing feature values from learning images not containing the target object for recognition, and thus the clothing feature values C₁ and M₁ are also taken to be errors.

In the example shown in FIG. 12, the threshold value th₁₁ is set such that the error rate e_(jk) is minimized. For example, when the threshold value th₁₁ shown in FIG. 12 is not positioned such that the error rate e_(jk) is minimized, the classifier configuration unit 54 varies the position of the threshold value th₁₁, and while checking the error rate e_(jk) at each position, searches for the position of the threshold value th₁₁ where the error rate e_(jk) is minimized. Once found, this position is taken to be the position of the threshold value th₁₁.

As shown in the following Eq. 7, the error rate calculator 54 a uses the hit/miss information (i.e., labels) of the learning images as a basis for calculating the error rate e_(jk) by adding together the weights Wi of the learning images from which the clothing feature values taken to be errors were extracted.

Eq. 7 e _(jk) =E _(w)[1_((y≠f) _(jk) ₎]  (7)

Herein, y≠f_(jk) represents the parameter whereby a pair k of clothing feature points becomes an error, while E_(W) indicates that the weights in the error-producing pairs k are to be added together.

In step S55, the classifier selector 55 uses the N error rate e_(jk) for each pair k supplied from the classifier configuration unit 54 as a basis for selecting, from among the N weak classifiers f_(jk), a weak classifier f_(jk) such that the error rate e_(jk) is minimized. The classifier selector 55 then acquires the selected weak classifier f_(jk) from the classifier configuration unit 54.

In step S56, the classifier selector 55 uses the error rate e_(jk) of the selected weak classifier f_(jk) as a basis for calculating the reliability factor c_(j) shown in the following Eq. 8. The calculated result is supplied to the weight updater 56.

Eq. 8 c _(j)=log((1−e _(j))/e _(j))  (8)

In Eq. 8, e_(j) represents the error rate e_(jk) of the weak classifier f_(jk) selected from among all error rates e_(jk). In other words, e_(j) represents the minimum e_(jk) among the N error rates e_(jk). Hereinafter, the weak classifier for the pair k selected in step S55 will be referred to as f_(j), and the error rate e_(jk) of this weak classifier f_(j) will be referred to as e_(j).

In step S57, the weight updater 56 evaluates the following Eq. 9 on the basis of the supplied reliability factor c_(j), thereby recalculating the weights Wi for each learning image PI_(i), while additionally normalizing and updating all weights Wi. The updated results are supplied to the weighting unit 52. On the basis of updated weight results supplied by the weight updater 56, the weighting unit 52 sets the weights for each learning image.

Eq. 9 w _(i) =w _(i)exp[−c _(j)·1_((y≠fj))], i=1, 2, . . . N  (9) Eq. 9 demonstrates that the weights Wi increase for learning images that contain error-producing clothing feature values.

In step S58, the classifier selector 55 uses the newly calculated weak classifiers f_(j) to update the stored clothing classifier R(x). In other words, the classifier selector 55 updates the clothing classifier R(x) by evaluating the following Eq. 10.

Eq. 10 R(x)=R′(x)+c _(j) ×f _(j)(x)  (10)

In Eq. 10, R′(x) represents the pre-update clothing classifier being stored by the classifier selector 55, while f_(j)(x) represents the newly calculated weak classifiers f_(j). In other words, the classifier selector 55 updates the clothing classifier by first taking the stored classifier, and adding to it the newly calculated weak classifier that has been weighted by multiplication with the reliability factor c_(j).

In step S59, the classifier selector 55 takes the clothing feature value for the pair k of clothing feature points corresponding to the weak classifier f_(jk) where the error rate e_(jk) is minimized, and stores this clothing feature value as the classification feature value.

In step S60, the classifier selector 55 determines whether or not the counter j is equal to or greater than L. If it is determined in step S60 that the counter j is not equal to or greater than L, then in step S61, the classifier selector 55 increments the counter j. Subsequently, the process returns to step S52, and the above processing is repeated.

In other words, using the newly-set weights Wi for each learning image, new weak classifiers f_(jk) are set for the N pairs k, and from these weak classifiers f_(jk) a single weak classifier f_(jk) is selected such that the error rate e_(jk) is minimized. The clothing classifier is then updated by the selected weak classifier f_(jk).

In contrast, if it is determined in step S60 that the counter j is equal to or greater than L, then in step S62, the classifier selector 55 outputs the stored clothing classifier and classification feature value to the ensemble classifier generator 27. Subsequently, the process proceeds to step S15 shown in FIG. 6.

As a result of the above process, a clothing classifier made up of L weak classifiers f_(i) (1≦j≦L) with comparatively low error rates is supplied to the ensemble classifier generator 27, while in addition, the clothing feature values for each pair k of clothing feature points to be used with each respective weak classifier f_(j) are also supplied to the ensemble classifier generator 27. Herein, L is taken to be less than N.

The clothing classifier from Eq. 10 is used to generate a classifier (i.e., a function) such that, when a clothing feature value is substituted in, a value of +1 is output when the clothing classifier is positive, and −1 is output when the clothing classifier is negative. Thus, this classifier is a function that outputs a yes or no regarding the target object to be recognized, determined by majority rule of the L weak classifiers. This learning process described with reference to the flowchart in FIG. 7, wherein weak classifiers are repeatedly weighted and summed to generate a classifier, is referred to as the discrete Adaboost algorithm.

In other words, as a result of the above clothing classifier generation process, processing to calculate weak classifiers and error rates for each pair of clothing feature points is repeated such that the weights of the clothing feature values for the learning images gradually increase with high error rates, and decrease with low error rates. Consequently, in the repeated processing (i.e., steps S52 to S61), when a clothing feature value is selected for setting a weak classifier (i.e., the clothing feature value selected in step S52), clothing feature values with high error rates become more readily selected over time. Learning is thus repeated with clothing feature values for which recognition is difficult being selected more often with increasing repetitions. For this reason, the clothing feature values in the learning image for which recognition is difficult become selected more often, thereby making it ultimately possible to increase the recognition rate.

Furthermore, in the repeated processing (i.e., steps S52 to S61), the classifier selector 55 selects the weak classifier corresponding to the pair with the lowest error rate. Thus, by repeating the learning process, the weak classifiers selected and added to the clothing classifier are for the pairs of clothing feature points with the highest reliability factors, and with each repetition a weak classifier with high accuracy is successively calculated.

Moreover, the clothing classifier is a classifier that uses the clothing feature values to determine whether or not an image contains a human set as the target object. The pairs of clothing feature points corresponding to the clothing feature values substituted into each weak classifier constituting the clothing classifier are thus the pairs best suited, from among all pairs of clothing feature points, to detect the target object from the input image.

For example, in FIG. 13, the pairs corresponding to the clothing feature values substituted into the clothing classifier are the pairs of clothing feature points surrounding the human in the image set as the target object. In FIG. 13, each straight, broken line connects two clothing feature points forming a pair, while the squares centered about the endpoints of each line represent the texture areas used when calculating the clothing feature values.

In the example shown in FIG. 13, there exists a pair for which the texture distance (i.e., the clothing feature value) decreases, being made up of two clothing feature points on the upper-body clothing worn by the human in the image. There also exists a pair for which the clothing feature value increases, being made up of a clothing feature point on the person's clothing, and a clothing feature point on the background rather than the person. The example shown in FIG. 13 thus demonstrates how pairs such as the above are selected.

Returning now to the flowchart in FIG. 6, in step S15, the contour feature point extractor 24 extracts contour feature points from the input learning image.

For example, when the learning image shown in FIG. 14A is input into the contour feature point extractor 24, the contour feature point extractor 24 extracts contour feature points in the form of pixels arranged in predetermined intervals in the learning image, as shown in FIG. 14B. In FIG. 14B, the circles on the learning image represent the pixels taken to be the contour feature points.

The learning images shown in FIGS. 14A and 14B are made up of 32 pixels in the horizontal direction and 64 pixels in the vertical direction. The contour feature points selected as contour feature points by the contour feature point extractor 24 are spaced at two-pixel intervals in the learning image in both the horizontal and vertical directions. As a result, 12 pixels in the horizontal direction and 28 pixels in the vertical direction as shown in FIG. 14B are selected in the learning image as contour feature points, for a total of 336 (12×28) pixels.

Upon extracting the contour feature points from the learning image, the contour feature point extractor 24 supplies the extracted contour feature points and the input learning image to the contour feature value calculator 25.

In step S16, the contour feature value calculator 25 conducts a contour feature value calculation process, wherein a contour feature value is calculated for each contour feature point on the basis of the contour feature points and the learning image supplied from the contour feature point extractor 24.

The contour feature value calculation process corresponding to step S16 will now be described with reference to the flowchart shown in FIG. 8.

In step S101, the contour feature value calculator 25 selects, or more specifically, the first-order filter processor 61, the second-order filter processor 62, and the third-order filter processor 63 of the contour feature value calculator 25 respectively select, a subject pixel in the form of a single unprocessed contour feature point from among the contour feature points supplied from the contour feature point extractor 24.

In step S102, the contour feature value calculator 25 sets a counter q indicating the direction θ_(q) to 1. In so doing, the direction θ_(q) is set to θ₁.

In step S103, the first-order filter processor 61 conducts first-order filtering. In other words, on the basis of the pixel value of the subject pixel to be processed, the first-order filter processor 61 evaluates Eq. 2, setting the Gaussian width σ to 1 (σ=1) and the direction to θ_(q). The filtered result is supplied to the feature value generator 64. In other words, Eq. 2 is evaluated with the direction θ set to θ_(q), and a contour is extracted.

It should be appreciated that while the above states that the Gaussian width σ is set to 1 (σ=1), in the case of the present embodiment, the Gaussian width is fixed at σ=1 (i.e., a filter of one Gaussian width is configured in advance). For this reason, it is possible to omit the processing to set the Gaussian width σ to 1. In other words, in the present embodiment, processing is executed in step S103 so as to evaluate Eq. 2 by applying a filter with a Gaussian width σ of 1 in a direction θ_(q). Hereinafter, the Gaussian width σ will continue to be described as being 1 (σ=1), but obviously the Gaussian width of the prepared filter may be a Gaussian width other than σ=1.

In step S104, the second-order filter processor 62 conducts second-order filtering. In other words, on the basis of the pixel value of the subject pixel, the second-order filter processor 62 evaluates Eq. 3 by applying a filter of Gaussian width σ=1 in the direction e_(q). The filtered result is supplied to the feature value generator 64. In other words, Eq. 3 is evaluated with the direction θ set to θ_(q), and a contour is extracted.

In step S105, the third-order filter processor 63 conducts third-order filtering. In other words, on the basis of the pixel value of the subject pixel, the third-order filter processor 63 evaluates Eq. 5 by applying a filter of Gaussian width σ=1 in the direction θ_(q). The filtered result is supplied to the feature value generator 64. In other words, Eq. 5 is evaluated with the direction θ set to θ_(q), and a contour is extracted.

In step S106, the contour feature value calculator 25 determines whether or not the direction θ_(q) is θ₄, or in other words, whether or not the counter q is equal to 4 (q=4). If it is determined in step S106 that the direction θ_(q) is not θ₄, then in step S107, the contour feature value calculator 25 increments the counter q. For example, if the counter q equals 1 (q=1), the counter q is incremented to 2 (q=2), thereby setting the direction θ_(q) to θ₂. Once the counter q has been incremented, the process returns to step S103, and the above processing is repeated.

In contrast, if it is determined in step S106 that the direction θ_(q) is θ₄, then in step S108, the feature value generator 64 combines the calculation results (i.e., contour feature values) supplied from the first-order filter processor 61, the second-order filter processor 62, and the third-order filter processor 63 to generate a contour feature value for a single contour feature point.

The contour feature value may be calculated according to the following Eqs. 11 or 12.

$\begin{matrix} {{Eq}.\mspace{14mu} 11} & \; \\ {\nu_{j} = {\sum\limits_{x,y}{{G_{d,\theta} \otimes {I\left( {x_{i},y_{i},s_{i}} \right)}}}}} & (11) \\ {{Eq}.\mspace{14mu} 12} & \; \\ {\nu_{j} = {\max\limits_{x,y}{{G_{d,\theta} \otimes {I\left( {x_{i},y_{i},s_{i}} \right)}}}}} & (12) \end{matrix}$

In Eqs. 11 and 12, G_(d,θ) is the d-th order derivative function of the Gaussian function G for an arbitrary angle θ, the same as that shown in Eq. 2. Additionally, in the term I(x_(i),y_(i),s_(i)), (x_(i),y_(i)) represents the in-image coordinates of the contour feature point being processed, while (s_(i)) represents the scale of the image being processed from among the images constituting the image pyramid.

Eq. 11 is a formula for first computing the tensor product of the contour feature values and the d-th order derivative function of the Gaussian function G for an arbitrary angle θ, and then computing the sum (Σ) of the absolute values of the result. Eq. 12 is a formula for computing the tensor product of the contour feature values and the d-th order derivative function of the Gaussian function G for an arbitrary angle θ, and then computing the maximum value (max) of the absolute values of the result.

Although Eqs. 11 and 12 are both formulas for computing a feature value, Eq. 11 is a formula for calculating local energy, while Eq. 12 is a formula for calculating the local maximum value. The meaning of these formulas will now be described.

As a result of processing like that described above, supervised statistical learning is conducted, using a function at an arbitrary angle and scale-extracted filter coefficients as feature values. In so doing, a detection classifier for detecting a human or similar target object can be generated. However, in this detection classifier, there exist feature values dependent on, for example, the clothing the person is wearing and his or her relationship with the background. Furthermore, feature value selectivity is highly non-constrained for recognition targets having significant deformation and transformation, like humans. Thus, it is desirable to conduct processing that absorbs such factors, and converts the respective feature values into invariant feature values.

The conversion from feature values dependent on the clothing a person is wearing and his or her relationship with the background to invariant feature values can be resolved by computing the absolute values of the filtered output values. By computing the absolute values, feature values close to a person's contours can be extracted. In the present embodiment, a first-order derivative function, a second-order derivative function, and additionally, a third-order derivative function are evaluated, with the respective absolute values taken from each. Thus, accuracy is significantly improved over the case of computing only the absolute values from a first-order derivative function, thereby enabling the extraction of invariant feature values.

As described above, feature value selectivity is highly non-constrained for recognition targets having significant deformation and transformation, like humans. Computation of feature values able to absorb this factor is enabled by performing position-invariant computations. For example, when the contours of a person's face are detected, the computations utilize factors such that the lengths of those contours are nearly the same regardless of the shape of the face. In other words, when focusing on a given portion of a contour, the computations regard values such as the length of that portion to be invariant, even when that portion shifts position. For example, if the contours of a person with a nearly round face changes position so as to overlap the contours of a person with a long and narrow face, then the computations regard the contours as having changed position only, while the lengths remain invariant.

Such computations involve computing the sum, as in Eq. 11. By computing the sum, the sum of the contours of a person's face is computed, for example. Alternatively, the maximum value may be computed, as in Eq. 12. By computing the maximum value, the maximum value from among those of the contours of a person's face is computed, for example.

Herein, two computations have been demonstrated: the sum and the maximum value. In other words, computation for calculating the local energy on the basis of Eq. 11 has been demonstrated, as well as computation for calculating the local maximum value on the basis of Eq. 12, as described above. In addition to these computations, computation may be conducted such that the local energy surrounding a point exhibiting a local maximum value is calculated. Such computation presumably involves taking the computational result from Eq. 12 and performing the computation in Eq. 11. Alternatively, computation may be conducted such that the maximum value near a local energy is calculated. Such computation presumably involves taking the computational result from Eq. 11 and performing the computation in Eq. 12. Although specific formulas are not given herein, feature values may be calculated with such computations.

By means of such computation, a feature value is calculated from each contour feature point. Subsequently, in step S109, the contour feature value calculator 25 determines whether or not processing has finished for all contour feature points. For example, if contour feature values have been calculated from all contour feature points supplied from the contour feature point extractor 24, then the processing is determined to be finished.

If it is determined in step S109 that processing has not finished for all contour feature points, then the process returns to step S101, and the next contour feature point is selected as the subject pixel.

In contrast, if it is determined in step S109 that processing has finished for all contour feature points, then the feature value generator 64 supplies both the learning image supplied from the contour feature point extractor 24 and the generated contour feature values for each contour feature point to the contour classifier generator 26. Subsequently, the process proceeds to step S17 in FIG. 6.

It should be appreciated that the extraction of contour feature values from the learning image is not limited to being conducted with a steerable filter, and a Gabor or similar filter may also be used.

Returning now to the flowchart shown in FIG. 6, once the contour feature values for each contour feature point have been calculated, in step S17 the contour classifier generator 26 uses the learning image and the contour feature values supplied from the contour feature value calculator 25 as a basis for conducting a contour classifier generation process, and thus generates a contour classifier. The contour classifier generation process herein is similar to the clothing classifier generation process described with reference to FIG. 7, and thus further description thereof is omitted.

More specifically, the contour classifier generation process differs from the clothing classifier generation process only in that the feature values to be processed are contour feature values, rather than clothing feature values. Consequently, in the contour classifier generation process, a contour classifier is generated from the sum of weak classifiers corresponding to the contour feature values of contour feature points having the lowest error rates. The contour classifier generator 26 supplies the generated contour classifier and classification feature values to the ensemble classifier generator 27.

In step S18, the ensemble classifier generator 27 generates an ensemble classifier by combining the clothing classifier supplied from the clothing classifier generator 23 with the contour classifier supplied from the contour classifier generator 26.

For example, since a classifier obtained by Adaboost-based statistical learning can be expressed as a linear combination of weak classifiers, the ensemble classifier generator 27 combines the clothing classifier and the contour classifier by late fusion.

More specifically, the ensemble classifier generator 27 calculates the classifier sum U(x) of the clothing classifier R(x) and the contour classifier T(x) by evaluating the following Eq. 13. In other words, the classifier sum U(x) is derived by a taking a linear combination of the clothing classifier R(x) and the contour classifier T(x).

Eq. 13 U(x)=α·R(x)+β·T(x)  (13)

In Eq. 13, α and β are predetermined constants (i.e., tuning parameters), and may be calculated using factors such as the classification rate with respect to the learning images used in the statistical learning, for example. The contour classifier T(x) is a sum of weak classifiers that have been multiplied by their reliability factors, and is similar to the clothing classifier R(x) shown in Eq. 10.

Additionally, the ensemble classifier generator 27 uses the calculated classifier sum U(x) to generate an ensemble classifier, as shown in the following Eq. 14.

Eq. 14 Ensemble classifier=sign(U(x))  (14)

In Eq. 14, when the classifier sum U(x) is positive, sign (U(x)) outputs +1, which indicates that the target object to be recognized exists within the input image. When the classifier sum U(x) is negative, sign(U(x)) outputs −1, which indicates that the target object to be recognized does not exist within the input image.

Upon generating an ensemble classifier in this way, the ensemble classifier generator 27 supplies the generated ensemble classifier to the classifier recording unit 12, where the ensemble classifier is recorded. In addition, the ensemble classifier generator 27 generates a final classification feature value by adding the classification feature values supplied from the contour classifier generator 26 to the classification feature values supplied from the clothing classifier generator 23. The final classification feature value is supplied to the classifier recording unit 12 and recorded, and the learning process is terminated.

In this way, the learning apparatus 11 extracts clothing feature points from a learning image, calculates a clothing feature value for each pair of clothing feature points, and generates a clothing classifier by means of statistical learning. In addition, the learning apparatus 11 also extracts contour feature points from the learning image, calculates contour feature values, and generates a contour classifier by means of statistical learning. Subsequently, the learning apparatus 11 combines the clothing classifier and the contour classifier in a linear combination to generate an ensemble classifier.

Thus, by combining the clothing classifier and the contour classifier and generating an ensemble classifier, an ensemble classifier able to reliably detect a target object from an image can be provided. In other words, since the ensemble classifier is an ensemble of a clothing classifier, which utilizes the clothing features of the target object, as well as a contour classifier, which utilizes the contours of the target object, the target object can be detected from the image if feature values of at least one type can be sufficiently extracted.

When detecting a person as the target object from an image, it is desirable to detect that person even if his or her clothing changes. For this reason, detection of humans from an image is conducted in the related art using only contours as feature values, which do not depend on the brightness of a person's clothing.

In contrast, the learning apparatus 11 uses clothing feature values for the detection of a human from an image that utilize the features of a person's clothing, but are themselves invariant with respect to changes in the pattern of the person's clothing. These clothing feature values are newly defined feature values exploiting the observation that, statistically, a person often wears repeating patterns of the same texture on his or her upper body (i.e., a shirt), while also wearing repeating patterns of the same texture on his or her lower body (i.e., pants).

In other words, the clothing feature values indicate the degree of resemblance (i.e., the similarity) between the textures (i.e., brightness patterns) in two arbitrary regions on the image. For example, the texture similarity may be high for two regions on the person's upper body, while the texture similarity may be low between the upper body and lower body, or between the person's clothing and the background. In the learning apparatus 11, such texture similarities between pairs of regions are utilized to generate a clothing classifier for detecting a human from an image, which is then used to generate the ensemble classifier.

Consequently, even if contours are not sufficiently extracted from the input image, for example, the ensemble classifier can still be used to detect a human from the image if texture similarity features between pairs of regions can be sufficiently extracted from the image. In contrast, if the clothing worn by the person has a non-repeating pattern, or when the clothing is partially concealed in the image by a bag or other object, then texture similarity features may not be sufficiently extracted from the image. However, if contours can be sufficiently extracted from the image, then the person can be detected from the image using the ensemble classifier.

[Recognition Process]

A process conducted when using the learning results to detect (i.e., recognize) a target object such as a human, for example, will now be described. An input image is input into the recognition apparatus 13, and when instructions to detect a human as the target object are issued, the recognition apparatus 13 initiates a human detection process, and detects the target object from the input image. Hereinafter, the human detection process executed by the recognition apparatus 13 will be described with reference to the flowchart shown in FIG. 15.

The processing respectively conducted in steps S150 to S153 is similar to the processing respectively conducting in steps S10 to S13 in FIG. 6, and thus further description is herein omitted. In other words, the clothing feature point extractor 31 extracts clothing feature points from the input image that was input above, while the clothing feature value calculator 32 pairs the clothing feature points extracted by the clothing feature point extractor 31, and then calculates a clothing feature value for each pair. Subsequently, the clothing feature value calculator 32 supplies the clothing feature values calculated for each pair to the classification calculator 35.

The image pyramid generator 30 is configured such that, when generating an image pyramid, images are generated at the same scales (i.e., resolutions) as those of the image pyramid generated by the image pyramid generator 20 in the learning apparatus 11. By matching the scale coefficients used for recognition with the scale coefficients used for learning, it becomes possible to efficiently perform scanning during recognition.

In step S154, the contour feature point extractor 33 executes processing similar to that in step S15 of FIG. 6. Contour feature points are extracted from the input image, and then supplied to the contour feature value calculator 34 together with the input image.

In step S155, the contour feature value calculator 34 uses the input image and the contour feature points from the contour feature point extractor 33 as a basis for conducting a contour feature value calculation process, and calculates a contour feature value for each contour feature point. Subsequently, the contour feature value calculator 34 supplies the calculated contour feature values to the classification calculator 35. The contour feature value calculation process herein is similar to the contour feature value calculation process described with reference to FIG. 8, and thus further description thereof is omitted.

In step S156, the classification calculator 35 reads both the classification feature values and the ensemble classifier from the classifier recording unit 12, substitutes the feature values into the ensemble classifier, and evaluates. More specifically, the classification calculator 35 substitutes values into the ensemble classifier shown in Eq. 14 that correspond to the classification feature values from among the clothing feature values supplied by the clothing feature value calculator 32 and the contour feature values supplied by the contour feature value calculator 34, and then evaluates the ensemble classifier.

At this point, the feature values substituted into the weak classifiers constituting the ensemble classifier are feature values calculated from a pair of clothing feature points or a contour feature point on the input image, wherein the points are located at the same positions as those of a pair of clothing feature points or a contour feature point from which feature values were calculated as classification feature values. Furthermore, the feature values taken to be classification feature values are those feature values that were used to set the weak classifiers constituting the ensemble classifier during the statistical learning process.

The computational result obtained upon evaluating Eq. 14 is either +1, which indicates that the person set as the target object exists within the input image, or −1, which indicates that the person set as the target object does not exist within the input image. The classification calculator 35 supplies the computational result from the ensemble classifier to the classification result output unit 36.

In step S157, the classification result output unit 36 outputs a detection result for the person on the basis of the computational result received from the classification calculator 35, and the human detection process is then terminated. In other words, a classification result is output, indicating whether or not the target object was recognized in the input image.

As one example of a classification result indicating whether or not a target object has been recognized in the input image, the classification result output unit 36 may be configured to display the input image with frames enclosing the regions where the target object (i.e., a person) was detected, as shown in FIG. 16.

The input image shown in FIG. 16 contains two persons set as target objects, and frames enclosing each person are displayed on the input image. In this case, the input image is input into the classification result output unit 36, while the classification calculator 35 supplies the computational result to the classification result output unit 36, together with information indicating the regions in the input image where the target objects were detected. Then, on the basis of the computational result and the region-indicating information supplied from the classification calculator 35, the classification result output unit 36 displays the input image together with frames enclosing the regions where the target object was found in the case where the target object was detected from the input image.

In this way, the recognition apparatus 13 extracts clothing feature points from an input image and calculates clothing feature values for pairs of clothing feature points, while additionally extracting contour feature points from the input image and calculating contour feature values. Subsequently, the recognition apparatus 13 detects a target object from the input image, using both the calculated clothing feature values and contour feature values, as well as the ensemble classifier recorded in the classifier recording unit 12.

Thus, by using clothing feature values and contour feature values to detect a target object from an input image, the target object can be more reliably detected from the image. In other words, the target object can be reliably detected from the input image if at least one type of either the clothing feature values or the contour feature values can be sufficiently extracted from the input image.

Although the foregoing describes detecting a human as the target object, it should be appreciated that the target object is not limited to be being a human, and may instead be any object whose surface pattern exhibits repeating patterns of the same textures.

Also, although the foregoing describes the example of executing a statistical learning process on the basis of the discrete Adaboost algorithm, other boosting algorithms may also be applied, such as the Gentle Adaboost algorithm. The discrete Adaboost algorithm differs from the Gentle Adaboost algorithm in that while the classifier output results of the former are discrete variates, the results of the latter are continuous variates. However, the former involves multiplication by a reliability factor, and thus the output results are treated as continuous variates in practice. For this reason, the two algorithms are essentially the same.

In addition to the above, clothing classifiers and contour classifiers may also be generated by conducting statistical learning according to support vector machine (SVM), Bayesian, or other methods. However, if the statistical learning process is configured such that feature values (i.e., clothing feature values or contour feature values) are selected by Adaboost, then processing can be executed at higher speeds when detecting a person using the ensemble classifier in the recognition apparatus 13.

Although the foregoing describes generating a clothing classifier and a contour classifier, and then combining these classifiers to generate an ensemble classifier, the ensemble classifier may also be generated directly from the clothing feature values and the contour feature values, without generating the clothing classifier and the contour classifier.

As described earlier, the input image is converted into several images at different resolutions (i.e., an image pyramid), and then these images at different resolution are respectively filtered. Doing so enables calculation efficiency to be improved, thereby enabling the processing speed to be improved. Consequently, it becomes possible to recognize target objects such as humans in real-time, for example.

For example, filtering images at a plurality of scales using a plurality of filters involves significant filter computation, leading to the possibility of greatly increased processing time or processing capability. However, in the present embodiment, images at a plurality of scales are filtered using a single filter. In other words, since convolution is conducted at just one scale, images can be filtered without significant computation, thereby enabling the processing speed to be improved.

Furthermore, in the case of a multi-scale filter, convolution operations are time-consuming at low frequencies (i.e., for large values of the Gaussian width σ). However, in the present embodiment, it is possible to form the filter at a single Gaussian width σ as described earlier. As a result, filtering is achieved without preparing a filter at a plurality of Gaussian widths, and without computing with filters at a plurality of Gaussian widths. Consequently, according to present embodiment, even it is assumed that processing is executed with a single filter prepared at the highest frequency, it is still possible to greatly improve the processing speed compared to the case of a multi-scale filter.

[Hand Shape Detection]

An example will now be described for the case of detecting humans as the target object in the embodiment described above. In order to detect humans, images capturing humans and images not capturing humans are used when conducting learning in the learning apparatus 11. As shown in FIG. 17, if learning is conducted in the learning apparatus 11 using hand images 201-1 to 201-M as well as nature images (i.e., images that are not hand images) 202-1 to 202-N, then it is possible to generate a classifier able to classify (i.e., detect) hands.

The images input into the learning apparatus 11 as the hand images 201 may be, for example, similar to the hand image 201 shown in FIG. 18. The hand image 201 is an image of a subject 211 exhibiting the hand gesture colloquially referred to as a peace sign. When generating a classifier for classifying a peace sign hand shape, learning is conducted using M hand images 201 containing an image portion of a hand making a peace sign as shown in FIG. 18. The images input into the learning apparatus 11 as the nature images are images wherein hand shapes do not appear. Learning is conducted using N such nature images.

By inputting a number (M+N) of hand images 201 and nature images 202 into the learning apparatus 11 and conducting learning, a classifier that classifies a predetermined hand shape is generated and stored in the classifier recording unit 12. This classifier is able to classify hand image portions and non-hand image portions from an input image. Furthermore, when learning is conducted using images of hands making peace signs as the hand images 201, for example, a classifier is generated that classifies hands in the shape of a peace sign. When learning is conducted using images of hands making fists as the hand images 201, a classifier is generated that classifies hands in the shape of a fist.

In other words, a classifier suited to the shape of the hand to be classified can be generated by means of the hand shapes in the hand images 201 used when learning.

As described earlier with reference to FIG. 1, the learning apparatus 11 is configured to include a clothing classifier generator 23 that generates a clothing classifier for distinguishing between images containing humans and images not containing humans from the features of the clothing worn by the humans, as well as a contour classifier generator 26 that generates a contour classifier for distinguishing between images containing humans and images not containing humans from the features of the contours of the humans.

Since the clothing classifier is generated by detecting clothing feature values from the cuffs or other portions of clothing, for example, the clothing classifier may conceivably function effectively as a classifier for distinguishing between images containing hands and images not containing hands. Furthermore, in the present embodiment, not only a clothing classifier, but also a contour classifier is generated. Hand contours can be detected by means of this contour classifier, and thus the contour classifier may also conceivably function effectively as a classifier for distinguishing images containing hands and images not containing hands. By means of the ensemble classifier generator 27, the clothing classifier and the contour classifier can be combined to generate a classifier for detecting hand shapes.

In the related art, methods have been proposed for extracting hand image portions from predetermined images and recognizing hand shapes by utilizing skin color and similar color features. However, an embodiment of the present invention detects hand shapes using feature values that are not dependent on color. Consequently, even hands covered in gloves or other material can be detected, for example. In other words, hands can be detected even from images where detection of hand color is problematic (such as black and white images, for example).

Furthermore, if gloves are considered to be clothing and there exists a statistical correlation in the texture relationship between two regions, then the clothing feature values also function effectively. Even if hand textures are considered, the texture difference between two regions is often small, and thus the hand textures themselves can also be used.

In this way, an embodiment of the present invention can be applied to generate a classifier for classifying hand shapes, which is able to accurately classify hand shapes similarly to the classifier for classifying humans described earlier. Furthermore, since the calculations conducted for classification are efficient, the processing speed can be improved.

An image processing apparatus will now be described wherein a classifier for classifying hand shapes generated as described above is used to classify a hand shape and obtain an image using the classification result. FIG. 19 illustrates a functional configuration of an image processing apparatus. The image processing apparatus 230 shown in FIG. 19 includes a classifier recording unit 12, a recognition apparatus 13, an image acquirer 231, a shutter controller 232, and an image storage unit 233.

The image processing apparatus 230 having a configuration like the above is incorporated into a device such as a digital still camera or digital video camera, for example. If the image processing apparatus 230 is incorporated into a digital still camera, then the image acquirer 231 is configured to include an image sensor or similar element. The image acquirer 231 thus obtains an image by imaging a subject.

The classifier recording unit 12 and the recognition apparatus 13 have functions respectively similar to the classifier recording unit 12 and the recognition apparatus 13 shown in FIG. 1, and are configured similarly. For this reason, identical reference numbers are used, and further description is herein omitted. As described earlier, according to the classifier recording unit 12 and the recognition apparatus 13, it is possible to improve both the calculation efficiency and the processing speed when detecting a target object such as a human from an input image. For this reason, acquired images can be processed in real-time even when the image processing apparatus 230 is incorporated into a digital still camera or similar device.

In the recognition apparatus 13, a hand shape is recognized (i.e., detected) as the target object. Once a hand shape is detected by the recognition apparatus 13, information indicating the detection is supplied to the shutter controller 232. The shutter controller 232 controls a shutter included in the image acquirer 231. The shutter is a camera exposure apparatus that opens for a fixed amount of time. Digital still cameras may contain electronic shutters or mechanical shutters. Once the shutter activates, the image obtained by the image acquirer 231 is supplied to and stored in the image storage unit 233. The image storage unit 233 is made up of a predetermined recording medium, and stores image data.

If the classifier recording unit 12 stores classifiers for respectively classifying a plurality of hand shapes, then the recognition apparatus 13 is configured as shown in FIG. 20. An input image 251 is supplied to hand shape recognizers 252-1 to 252-N. The hand shape recognizers 252-1 to 252-N respectively include classifiers for classifying different hand shapes. The different hand shapes may include, for example, peace sign shapes, as well as the three hand shapes used in the game rock, paper, scissors. The classifiers for classifying the different hand shapes are stored in the classifier recording unit 12. The recognition apparatus 13 (i.e., the hand shape recognizers 252-1 to 252-N) then conduct classification using the respective classifiers.

As described with reference to FIG. 1, a plurality of classifiers are stored in the classifier recording unit 12. The classification calculator 35 in the recognition apparatus 13 conducts classification using the plurality of classifiers stored in the classifier recording unit 12. In other words, the hand shape recognizers 252-1 to 252-N are realized as a result of the classification calculator 35 performing calculations with different classifiers.

Returning now to FIG. 20, the detection results 253-1 to 253-N respectively output from the hand shape recognizers 252-1 to 252-N are supplied to a maximum value output recognizer 254. The maximum value output recognizer 254 recognizes the detection result 253 having the maximum value from among all the detection results 253-1 to 253-N. The maximum value output recognizer 254 outputs the recognition result to the shutter controller 232 (FIG. 19). When the recognition result is a predetermined hand shape, the shutter controller 232 controls the image acquirer 231 so as to acquire an image, and then store the acquired image in the image storage unit 233.

Such operation will now be further described with reference to the flowchart shown in FIG. 21. In step S211, an image is acquired. The image acquirer 231 conducts imaging using its internal image sensor. In a digital still camera, for example, this state involves the camera operator viewing an image of the subject displayed on the display of the digital still camera in order to decide on factors such as the composition of the shot. Additionally, this state also involves data being read from the image sensor of the image acquirer 231 and supplied to the display.

An image thus acquired is supplied to the display and presented to the user, while also being supplied to the recognition apparatus 13. In step S212, the recognition apparatus 13 detects a hand shape from the supplied image. For example, if a hand image 201 like that shown in FIG. 18 is supplied, then the region 212 is detected as the hand shape. This hand shape in this region 212 is then classified by determining which classifier classified the region.

For example, assume that the hand shape recognizer 252-1 is a classifier for detecting a peace sign. If the recognition result output by the maximum value output recognizer 254 is the detection result 253-1 from the hand shape recognizer 252-1, then it is detected that the hand image 201 contains an image portion classifiable as a hand, and furthermore that the image portion is that of a peace sign. In this way, the recognition apparatus 13 supplies the shutter controller 232 with a recognition result indicating the type of hand shape that was detected.

In step S213, the shutter controller 232 determines whether or not the hand shape is a predetermined hand shape. For example, the user may have registered a particular hand shape (herein, the shape of a peace sign) for when the shutter is activated. Information indicating that a peace sign shape has been registered is stored in the shutter controller 232. In step S213, the shutter controller 232 references the information and determines whether or not the hand shape indicated by the recognition result from the recognition apparatus 13 matches the registered hand shape.

Note that it is possible to omit the processing described above as registration if, for example, just a classifier for detecting a peace sign hand shape is stored in the classifier recording unit 12 (i.e., if the recognition apparatus 13 is configured to detect only a predetermined hand shape). The recognition apparatus 13 may then supply the shutter controller 232 with a recognition result indicating whether or not the predetermined hand shape was detected. The shutter controller 232 then executes the processing in step S213 by determining whether or not the recognition result indicates that the predetermined hand shape was detected.

If the shutter controller 232 determines in step S213 that the hand shape contained in the acquired image is not the predetermined hand shape, then the process returns to step S211 and repeats. In other words, image acquisition by the image acquirer 231 is continued until an image portion of a hand is contained in the image acquired by the image acquirer 231, and it is determined that the hand shape is the predetermined shape. The continuation of image acquisition by the image acquirer 231 is a state wherein the shutter is not activated and wherein images are not stored in the image storage unit 233. Rather, the state involves acquired image data being output from the image sensor of the image acquirer 231, as described earlier.

In contrast, if the shutter controller 232 determines in step S213 that that the shape of the hand contained in the acquired image is the predetermined shape, then the process proceeds to step S214. In step S214, the shutter controller 232 issues instructions causing the image acquirer 231 to activate the shutter, acquire an image, and then supply the acquired image to the image storage unit 233. On the basis of the instructions, the image acquirer 231 controls the electronic or other type of shutter, activates the shutter, and acquires an image. In step S215, the acquired image is supplied from the image acquirer 231 to the image storage unit 233 and stored therein.

By controlling the timing of shutter activation in this way, it becomes possible to acquire and store an image of the subject only when the subject exhibits a predetermined hand shape such as a peace sign, for example.

The foregoing series of processes may be executed by means of hardware or software. In the case of executing the series of processes by means of software, a program constituting such software may be installed on a computer built into special-purpose hardware. Alternatively, the program may be installed from a program recording medium onto a general-purpose computer (such as a personal computer, for example) capable of executing various functions by installing various programs thereon.

FIG. 22 is a block diagram illustrating an exemplary hardware configuration of a computer that executes the foregoing series of processes by means of a program.

In the computer, a CPU (Central Processing Unit) 501, ROM (Read-Only Memory) 502, and RAM (Random Access Memory) 503 are mutually connected by a bus 504.

The bus 504 is additionally connected to an input/output interface 505. The input/output interface 505 is connected to: an input unit 506 made up of components such as a keyboard, mouse, a microphone; an output unit 507 made up components such as a display and one or more speakers; a recording unit 508 made up of components such as a hard disk and non-volatile memory; a communication unit 509 made up of components such as a network interface; and a drive 510 that drives a removable medium 511, such as an optical disc, a magneto-optical disc, or semiconductor memory.

In the computer configured as described above, the CPU 501 may, for example, execute a program recorded in the recording unit 508 by loading the program into the RAM 503 via the input/output interface 505 and the bus 504. In so doing, the foregoing series of processes is conducted.

The program executed by the computer (i.e., the CPU 501) may be recorded onto the removable medium 511, being packaged media realized by magnetic disks (including flexible disks), optical discs (including CD-ROMs (Compact Discs Read-Only Memory) and DVDs (Digital Versatile Discs)), magneto-optical discs, or semiconductor memory. Alternatively, the program may be provided via a wired or wireless transmission medium such as a local area network, the Internet, or a digital satellite broadcast.

The program can be installed in the recording unit 508 via the input/output interface 505 by loading the removable medium 511 into the drive 510. Alternatively, the program can be received by the communication unit 509 via a wired or wireless transmission medium, and then installed in the recording unit 508. In addition to the above, the program may be installed in advance in the ROM 502 or the recording unit 508.

It should also be appreciated that the program executed by the computer may be a program wherein processes are conducted in a time series following the order described in the present specification, or a program wherein processes are conducted in parallel or at appropriate timings, such as when called.

The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-258011 filed in the Japan Patent Office on Oct. 3, 2008, and in Japanese Priority Patent Application JP 2009-055062 filed in the Japan Patent Office on Mar. 9, 2009, the entire content of which is hereby incorporated by reference.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 

What is claimed is:
 1. A learning apparatus, comprising: generating means configured to generate, from an input image, images having differing scale coefficients; extracting means configured to extract clothing feature points and contour feature points from each image generated by the generating means; calculating means configured to calculate feature values for the feature points by filtering the feature points using a predetermined filter; and a plurality of classifier generating means configured to generate one or more classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values, wherein the plurality of classifier generating means comprises a clothing classifier generating means generating a clothing classifier, a contour classifier generating means generating a contour classifier, and an ensemble classifier generating means generating an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the calculating means calculates clothing feature values for the clothing classifier by pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 2. The learning apparatus according to claim 1, wherein the predetermined filter is a derivative function having a predetermined Gaussian width.
 3. The learning apparatus according to claim 1, wherein the calculating means executes a plurality of convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, calculates a plurality of convolution results based on the derivative functions, and calculates a sum of absolute values corresponding to the plurality of convolution results.
 4. The learning apparatus according to claim 1, wherein the calculating means executes a plurality of convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, calculates a plurality of convolution results based on the derivative functions, and calculates a maximum absolute value corresponding to the plurality of convolution results.
 5. The learning apparatus according to claim 1, wherein the scale coefficients of the images used when classifying the predetermined target object using the plurality of classifiers are identical to the scale coefficients in the generating means.
 6. The learning apparatus according to claim 1, wherein the input image is an image containing an image of a predetermined hand shape, or alternatively, an image not containing an image of a hand, and the plurality of classifiers are classifiers for detecting a predetermined hand shape.
 7. A learning method, comprising the steps of: generating, from an input image, images having differing scale coefficients; extracting clothing feature points and contour feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and generating a plurality of classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values, wherein the plurality of classifiers comprises a clothing classifier, a contour classifier, and an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the calculating comprises pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 8. A nontransitory computer readable medium having encoded thereon a computer-readable program executing processing comprising the steps of: generating, from an input image, images having differing scale coefficients; extracting clothing feature points and contour feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and generating a plurality of classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values, wherein the plurality of classifiers comprises a clothing classifier, a contour classifier, and an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the calculating comprises pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 9. A recognition apparatus, comprising: generating means configured to generate, from an input image, images having differing scale coefficients; extracting means configured to extract clothing feature points and contour feature points from each image generated by the generating means; calculating means configured to calculate feature values for the feature points by filtering the feature points using a predetermined filter; and detecting means configured to detect a predetermined target object from the input image by substituting the feature values into a plurality of classifiers obtained by statistical learning and used for detecting a target object from an image, wherein the plurality of classifiers comprises a clothing classifier, a contour classifier, and an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the calculating means calculates clothing feature values for the clothing classifier by pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 10. The recognition apparatus according to claim 9, wherein the predetermined filter is a derivative function having a predetermined Gaussian width.
 11. The recognition apparatus according to claim 9, wherein the calculating means executes a plurality of convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, calculates a plurality of convolution results based on the derivative functions, and calculates a sum of absolute values corresponding to the plurality of convolution results.
 12. The recognition apparatus according to claim 9, wherein the calculating means executes a plurality of convolution operations involving derivative functions of predetermined order of a Gaussian function at an arbitrary angle, calculates a plurality of convolution results based on the derivative functions, and calculates a maximum absolute value corresponding to the plurality of convolution results.
 13. The recognition apparatus according to claim 9, wherein the a plurality of classifiers are classifiers for detecting a predetermined hand shape, and the input image is stored when the predetermined hand shape is detected by the detecting means.
 14. A recognition method, comprising the steps of: generating, from an input image, images having differing scale coefficients; extracting clothing feature points and contour feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and detecting a predetermined target object from the input image by substituting the feature values into a plurality of classifiers obtained by statistical learning and used for detecting a target object from an image, wherein the plurality of classifiers comprises a clothing classifier, a contour classifier, and an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the calculating comprises pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 15. A nontransitory computer readable medium having encoded thereon a program causing a computer to execute processing comprising the steps of: generating, from an input image, images having differing scale coefficients; extracting clothing feature points and contour feature points from each generated image; calculating feature values for the feature points by filtering the feature points using a predetermined filter; and detecting a predetermined target object from the input image by substituting the feature values into a plurality of classifiers obtained by statistical learning and used for detecting a target object from an image, wherein the plurality of classifiers comprises a clothing classifier, a contour classifier, and an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the calculating comprises pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 16. A learning apparatus, comprising: an image generator configured to generate, from an input image, images having differing scale coefficients; a feature point extractor configured to extract clothing feature points and contour feature points from each image generated by the image generator; a feature value calculator configured to calculate feature values for the feature points by filtering the feature points using a predetermined filter; and a plurality of classifier generators configured to generate a plurality of classifiers for detecting a predetermined target object from an image by means of statistical learning using the feature values, wherein the plurality of classifier generators comprises a clothing classifier generator generating a clothing classifier, a contour classifier generator generating a contour classifier, and an ensemble classifier generator generating an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the feature value calculator calculates clothing feature values for the clothing classifier by pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii.
 17. A recognition apparatus, comprising: an image generator configured to generate, from an input image, images having differing scale coefficients; a feature point extractor configured to extract clothing feature points and contour feature points from each image generated by the image generator; a feature value calculator configured to calculate feature values for the feature points by filtering the feature points using a predetermined filter; and a detector configured to detect a predetermined target object from the input image by substituting the feature values into a plurality of classifiers obtained by statistical learning and used for detecting a target object from an image, wherein the plurality of classifiers comprises a clothing classifier, a contour classifier, and an ensemble classifier, the ensemble classifier comprising a combination of the clothing classifier and the contour classifier, and wherein the feature value calculator calculates clothing feature values for the clothing classifier by pairing each extracted clothing feature point with each other extracted clothing feature point within a predetermined range of radii. 